Dynamic automatic traffic analyzer controller



Feb. 25, 1958 M. L. ERNST A 2,825,054

DYNAMIC AUTOMATIC TRAFFIC ANALYZER CONTROLLER Feb. 25, 1958 M. L. ERNST V2,825,054

` DYNAMIC UTOMATC TRAFFIC ANALYZER CONTROLLER Filed Sept. l5, 1953 11 Sheets-sheet 2 Feb. 25, 1958 M. L.. ERNST v 2,825,054

DYNAMIC AUTOMATIC TRAFFIC NALYZER CONTROLLER Filed sept. 15, 195s l1 Sheets-Sheet 3 fa l/Z INVENTOR. /WW/V l, EPA/57 Feb. 25, 1958 M. l.. ERNST 2,825,054

DYNAMIC AUTOMATIC TRAFFIC ANALYZER CONTROLLER Filed Sept. 15, 1955 1l Shee''sfshtaerI 4 Jaffa/M6 ,wf/faf M7/7.5) INVENTOR.

M. L. ERNST DYNAMIC AUTOMATIC TRAFFIC ANALYZER CONTROLLER INVENTOR. MAW/fw z. fin/.ff

Feb. 25, 1958 Filed Sept. l5, 1953 M. L. ERNST Feb.25,195s

DYNAMIC AUTOMATIC TRAFFIC ANALYZER CONTROLLER Filed Sept. l5, 1953 l1 Sheets-Sheet 6 INVENTOR. AMK/0V z. EPA/.57' v M. L. ERNST Feb. '25, 1958 DYNAMIC AUTOMATIC TRAFFIC ANALYZER CONTROLLER Filed Sept. 15, 1953 11 Sheets-Sheet 7 Y Feb. 25, 1958 Y Mfl.. ERNST 2,825,054

DYNAMIC AUTOMATIC TRAFFIC ANALYZER CONTROLLER Filed Sept. l5. 1953 11 Sheets-Sheet 8 fhA aaa@ #n /Df/ A P/Z 4 1LT-Cl 17D INVENTOR.

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fvg@ WMM U 5' M M. L. ERNST DYNMIC AUTOMATIC TRAFFIC ANALYZER CONTROLLER Filed Sept. 15, 1953 y 11 Sheets-Sheet 9 Feb. 25, 1958 M. L. ERNST 2,825,054

DYNAMIC AUTOMATIC TRAFFIC ANALYZER CONTROLLER l Filed sept. 15, 195s 11 sheets-sheet 1o l Feb. 25, 1958 M L. ERNST 2,825,054

DYNAMIC AUTOMATIC TRAFFIC ANALYZER CONTROLLER Filed Sept. l5, 1953 l 11 Sheets-Sheet 11 Ill ""III afb Eyym: A

United States Patent C DYNAMIC AUTOMATIC TRAFFIC ANALYZER CONTROLLER Martin L. Ernst, Washington, D. C.

Application September 15, 1953, Serial No. 380,382 18 Claims. (Cl. 343-6) (Granted under Title 315,y S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or fo-r the Government for governmental purposes without payment to me of any royalty thereon.

This invention relates to air traic control. Such control may be divided into three phases:

(1) The collection of data and other pertinent information, including the positions, velocities, courses, etc., on all aircraft in the region under control. V

(2) The assimilation of this data and its use in determining the procedures to be followed.

(3) The transmission of information to aircraft andits presentation therein so that they may carry out the adopted procedures. M

This invention relates to the second of the above phases. The first phase may be accomplished by a volumetric radar system, while the third phase may be carried out with any suitable radio transmission means capable of handling the amount of information required, and by any suitable presentation apparatus in the aircraft.

Two types of automatic traffic control procedures which have been proposed in the past are generally termedthe fixed-block and the moving-block systems. Both of these methods suffer from a number of inherent faults, based mainly upon their inexibility, some of which are (l) they require either fixed points of entry to and exit from the control area, the use of human control over portions of the tracks, or the development. of automatic computers to feed aircraft into the proper blocks; (2) they require trafc patterns of extreme complexity or they will be unable to cope with all the situations likely to be encountered; (3) they require continuous and very critical spacing control by each aircraft, and since a ixed path in space is employed, spacing control is forced to rely on the least eicient control parameter air speed; (4) the systems are extremely sensitive to the presence of uncontrolled aircraft; and (5) the systems do not immediately lend themselves to the most usable form of instrumentation, as the primary data consists of positional error rather than corrective-action information.

The weaknesses of the block systems are fundamentally determined by their adoption of rigid paths in both space and time. It is the object of this invention to provide a computer for a more flexible traffic control system based on the availability of a choice of paths in the four-V dimensional continuum. This choice permits selection, after consideration of all relevant factors, of the optimum approach path for each aircraft under control. In addition this inherent flexibility makes possible a procedure for continuously making efficient corrections for the small unavoidable errors which are always present in ilight. Further objects of the invention are to provide a computer giving coverage over the entire control area and providing traic solutions in the form of corrective instructions. Finally, it is also the object of the invention to provide a traffic computer having excellent characteristics for military use, such as: a minimum amount of airborne equipment, the ability to provide the swiftest possible i, 2,825,054 Patented' Feb. 25, 1-95'8 ICC approach paths for emergency aircraft,` the ability to operate effectively in bases remote from any other traffic control system, andV the provision of aminimum amount of information to any listening enemy.

The fundamental manner in which the idescribed Dynamic Automatic TraicAnalyzer-Controller, hereinafter referred to as DATAC, differs from other proposed traffic control procedures lies in the use of dynamic, rather than xed, approach paths. The importance of this feature is derived from the factV that it enables the aircraft to make use of'their easiest and most natural methods of maneuver. In effect, the trafiiccon'trolsystem is designed to tit the characteristics of aircraft in flight. Torthe greatest degree possible all=DATAC actions are comparable to those which would be taken by a pilot operating under ideal conditions. l

The DATAC, of which there will be one for each air'- craft under control, consists of three parts, namely; a First Sequence Unit, a Second Sequence Unit and a Master Sequencing Unit. The construction andl function of these various parts will be explained in connection with the accompanying drawings inV which:

Fig. l shows in block form a complete DATAC airv traiiic control system; v

Fig. 2 shows the possible starting positions for aircraft brought under DATAC control; l

Fig'. 3 shows the directV pattern night characteristics;

Figs. 4ab show typical approach patterns;

Figs.` Sabcd'illustrate offset angle and switch operations;

Fig. 6 shows the `FirstSequencc Unit;

Figs 7ab show the construction of Area B contacts in the First Sequence Unit; p

Fig. 8 shows a block diagram of the SecondfSequence Unit;

Fig. 9 illustratesV thel relationships used in the Position- Course, Distance and Time Computer;

Fig. l0 is a schematic diagram of the Positior'r-Cou'rse,l Distance and Time Computer;

Figs. 1l, 12`, 14, l5 and 1`6 show potentiometer characteristics in the PositionCourse, Distance and. Time Computer;

Fig. 13 shows the characteristic of Servo No. 1 Vin the Position-Course, Distancearnd Time Computer;

Fig. 17v is Va schematic diagram of the Schedule Cornputer;

Fig. 17a shows the construction of the clock-driven potentiometers `of Fig. 17.

Fig. 18` isa schematic diagram of the Schedule yCorrecti'on Computer;

Fig. 19 shows the Master Sequencing Unit;

Fig. 20 shows the Signal Selector Unit;

Fig'. 2l shows the construction of the Course Coding Commutator of the Signal Selector Unit.

Fig. 22 shows schematically the course computing and coding portion of the Signal Selector Unit;

Fig. 23 shows the altitude codingcommutator and associated circuit of the Signal Selector Unit;

Fig. 24 shows the speed coding commutator and associated circuit of the Signal Selector Unit; and

Fig. 25 Vshows a Amodification of the course coding circuit to permit transmission of rate-of-change course information. Y

Fig. l shows the type of air traHic control system in which the DATAC described herein would normally be used. It consists of a volumetric radar system 20 which collects three-dimensional data on aircraft in the control area and applies this data toa series of automatic trackingunitsZl. Each of the tracking-units has an output consisting of data applying to a single specific aircraft only. `The apparatus indicated generally at 22v determines, by meansof IFF, beacons, directionfmding Aor other methods, the identity of the various aircraft and their intentions or desires.V If an aircraft wishes to 'land it is assigned a DATAC channel 23, there being one DATAC channel for each aircraft under control. The DATAC thus assigned to the aircraft then determines the safest and most efficient procedures for controlling the aircraft from its identification position to a specific location, termed the Turn-On point, about 5 to 8 miles downwind of the runway, and transmits the necessary instructions to effect this maneuver to the aircraft over one of the channels of a suitable radio communications system 24.

The first problem to be encountered by the DATAC is one of ensuring that newly reporting planes are in suitable positions from which to start their approaches. Unsuitable positions include those occupied by aircraft which are too close to the field so that their maneuvers will interfere with the normal trafiic patterns, those of aircraft which are` in unsuitable areas so that their approaches will cross directly over the take-off pattern or the radar set, and those occupied by aircraft which are too high to make an approach with a standardvrate of descent. y

Once a plane is correctly positioned for an approach, the DATAC solves several problems. The first of these is to insure adequate time-spacing of aircraft. The most critical point, at which this spacing must be most accurate, is the turn-on point where aircraft turn onto and start fiying their final approaches. At all other places, the difference of aircraft air speeds may make passing desirable and therefore dictates the use of space rather than time separations.V From the turn-on point to touchdown, however, the aircraft must y straight, accurate vpaths and passing must be forbidden. In all cases, the

characteristics of the air field in use determines the minimum separation time between successive landing aircraft which must be exceeded if safe conditions are to exist. If an allowance for errors is added to the minimum separation time, an optimum spacing `time is obtained. The DATAC makes use of a series of discrete, permissible times of arrival at the turn-on point based on an arbitrary schedule. For example, if the optimum spacing is 11/2 minutes, with l0 seconds allowable error, aircraft are always scheduled to pass the turn-on point between seconds before and 10 seconds after multiples of ll/z minutes. While this procedure is not acompletely dynamic one, its use greatly simplifies the problem.

When a plane has been assigned the earliest possible turn-on arrival time, which must not conflict with that of any other aircraft, the DATAC determines thepath in space and time which the aircraft should follow. In establishing an approach path Vthe computer uses both course control and air speed, or, in other words, both space and time. There are essentially an infinite number of possible paths. The computer selects one ofthese in accordance with a standard procedure. As long as the aircraft correctly follows instructions the selected path will be used. If, however, the plane makes an error, the computer merely considers the situation as a new problem and determines a new path in accordance with the general procedure previously used.

The DATAC solves all situations in terms of what each .aircraft should do, and therefore its solutions are of the most desirable type from the standpoint of usability. In cases where the transmitted information is to be fed directly into the automatic pilot a change of course is sent as a rate of turn and a change of altitude as a rate of descent or ascent. In cases where flight information is to be displayed to the pilot, rather than'being fed directly to the automatic pilot, it is preferable to transmit the correct course to be flown rather than a rate of turn. Altitude information as a rate, however, is suitable for manual as well as automatic control.

1n performing the function briefly outlined above the overall action of a DATAC unit may be divided into three principal phases or sequences: the first or starting sequence involves ensuring that the aircraft iS, in; a, llabl@ vdifficulty by known methods.

position from which to make an approach; the second or main sequence carries out the approach until the aircraft is turned over to the final landing aid at a position, the turn-on point, 5 to 8 miles downwind of the runway; the third or final sequence is concerned mainly with missed final approaches and other special emergencies occurring while the aircraft is under control of the landing aid.

The input information which each DATAC unit receives from the volumetric radar and tracking units, shown in Fig. 1, is as follows:

(l) Aircraft range and azimuth coordinates measured from the turn-on point (Fig. 2) with the azimuth offset so that zero azimuth is aligned with the runway, making the approach path at zero degrees from the turn-on point, the primary data being in the form of angular displacements of rotating shafts.

(2) Aircraft ground speed in the form of steady voltages. In addition, standard air speed depending only on aircraft type, is set in manually.

(3) Altitude in the form of steady D. C. voltages.

(4) Aircraft course in the form of a steady voltage. Two features of the data requirements stated above need further comment. First, since the range and azimuth are measured from a specific point other than the location of the radar set, a change in coordinates of the radar data is necessary. This can be done without great Problems of multiple air fields or runways merely involve use of different coordinate changes. DATACs may either be set up for the different final approaches on a semipermanent basis, or may be continually altered according to traffic requirements.

The DATAC computer delivers to the data transmitters electrical signals providing discrete, specific flight instructions.

The above mentioned three sequences of DATAC operation will now be described in more detail:

F rst sequence The existence of regions which do not provide suitable positions from which to start approaches has been previously noted. The areas shown in Fig. 2 are determined rather arbitrarily, but are believed to be the simplest which meet all requirements. To prevent interference during the critical positions of the traffic patterns, Area A is chosen with the turn-on point (the point of highest aircraft concentration) at its center. Its radius is selected to include the turns to the final approach, the final approach and landing regions, and the first few miles of the take-off and go-around patterns. For a 6-mile final approach, a suitable radius for Area A is l2 miles. Area B Vmust be such that the most direct flight patterns from positions just outside it will not bring planes too close to the field or the radar set. These conditions are most easily met by having its width the same as the diameter of Area A.

l If an aircraft is first identified within Area A, it is desirable to remove it from that region as soon as possible. This is done most simply by having it fly the reciprocal of its bearing to the turn-on point, from which 0 (Fig. 2) is measured. For Area B a choice is possible; all the aircraft may be directed along a course of 270 or else they may fly either 90 or 270, depending on their positions Within the area. The former solution is preferable because it is simpler and it will permit more pilots to make the preferred left turns to the final approach. h

The problem of ensuring suitable starting altitudes 1s complicated by the fact that the permissible altitude' for a given position is a function of the pattern fiight-tlme, a quantity which cannot be determined at this stage o f the operation. It is therefore necessary to have the maximum starting altitude 'a function of range. This procedure neglects the range of air speeds which will be encountered, but also assumes a direct approach without 5 deviationsl A fairly'. safe criterion, whi'chshould'permit evenvery high speed aircraft to descend at reasonable rates, is to set the maximum altitude (feet) equal-to 1200+200r (miles), the constant 1200 equalling the proper altitude at the turn-on point where r=0. If an aircraft is above this altitude, or if it is below the minimum permissible altitude, 100i', it must take corrective action before it can proceed to` the next sequence. -summarizing the actions of the first sequence:

1) Aircraft are permitted to move to the second sequence only when they are outside Areas A and B, and are within the specified altitude limits.

(2) Aircraft in Area A are given courses =0 degrees to ily (see Fig. 3).

(3) Aircraft in Area B are given a course of 270 to fly.

(4) Aircraft with altitudes (feet) above 1200+200r, where r is in miles, are ordered to descend.

(5) Aircraft with altitudes below 1001' arev given instructions to climb.

Second Sequence As soon as control passes to the second sequence a number of sub-computers begin to function. The actions of these computers are as follows, with reference to Fig. 3:

(a) A Position-Course computer determines the direct-pattern flight heading (qd) for the aircraft, as a function of its momentary position. This heading must be tangent to a circular final turn which ensures that the aircraft is properly aligned when it passes the turn-on point. Normally, dierent types of aircraft would prefer the use of final turns of different radii but, for simplicity, a standard turn with a radius large enough (3 miles) for high speed planes is used.

(b) .A Position-Distance computer determines the length of the direct flight pattern (d).

(c) vThe direct-pattern flight VAtime (td) is determined from d and the aircraft velocity. To avoid fluctuations which radar determined velocity might introduce, the cruising speed with wind correction (v) of the type of aircraft in question may be used.

(d) Of the various discrete, permissible arrival times a Schedule Computer selects the earliest unoccupied one for which the time-to-go is greater than td minutes. After the. arrival time has been selected, the computer diminishes. This initial time-togo in step with the passage of time so as to continuously present the remaining timefto-go (ts) until the scheduled arrival time. Emergency aircraft may be assigned the earliest possible arrival time even at the expense of displacing other aircraft.

The computers described above provide four vbasic pieces of data: the direct-pattern heading (qid), the direct-pattern distance (d), the direct-pattern flight time (td), and the scheduled time-to-go (ts). These data are used to determine a suitable path in space and time for Vthe aircraft to follow. Since. variation of `air speed is'both an ineicient procedure and a relatively difficult one for pilots to follow, the major control parameter is the flight course. Excess time may be consumed with course variation by two means: (l) orbiting, and (2) flying an indirect route. Orbiting has the advantage of keeping anV aircraft in the same general position with respect to the airfield 'while large amounts of time can be spent, but .suffers from a disadvantage in that time must be used up in discrete units of about 2 minutes (for a complete orbit). An indirect course procedure is more flexible in that any desired amount of time may bespent; but it requires continual and often extensive changes of aircraft positions, which may introduce certaindifliculties. A combination of the two methods is used, `thereby incorporating the best features of each.

an aircraft fly at a specific angle with'res'pec't to the dil rect-pattern heading (pd). If. the schedule correction angle measured from the direct pattern heading (pd), is made a function of the ratio R=t,/td, approach paths conforming to almost any desired features can be obtained. In general it is desirable to use a pattern which keeps aircraft at a great range as long as possible, since this minimizes both the azimuth covered by the overall track, and the maximum concentration of aircraft per unit area. It also decreases the danger of the path becoming a spiral as the value of td becomes small. Figs. 4a and 4b show two patterns using different relationships between and R. Pattern 2 is unsuitable because of 1) the great range of azimuths traversed, (2) a tendency to spiral, and (3) the sharp turn required at the end of the track.

Two further steps are desirable to protect the offsetcourse technique from being rendered ineffective. `The first of these is a system of switches to change the sign of the offset angle ,8. These will reverse the direction of travel at suitable positions, and prevent aircraft from traversing excessive ranges of azimuth. Whenever is large, the reversal will involve a great change of course (up to 180 degrees), but this will happen only when considerable time can be spared. When R approaches unity and little time can be wasted, the change of course will be small. The second safety measure arises from the need to avoid any tendency either to spiral or to require sharp turns when td approaches zero. This is done by having the mechanism cease to operate when t'd reaches a low value, such as 1 minute (or when the. range is about 2 miles). At that time if the ratio Rv is within certain limits the run is successful; otherwise the operation has failed and must be repeated.

Figs. 5ft-5d illustrate the above described offset-course technique. Fig. 5a shows the relationship between the direct pattern flight heading (glad) and the offset or schedule correction angle for aircraft A1 and A2. Fig. 5b shows offset courses for two aircraft A1 and A2 in which reversalsr of the sign of ,B occur at 6=240 and 0:120" respectively. Fic. 5c illustrates the fact that when is large, approaching its maximum value of 90, the change in course, which approximately equals twice appreaches 180 or a complete reversal. Fig. 5d illustrates a case where is small and a correspondingly Y small course change is required.

An indirect course is most easily obtained byv havingA The adopted procedure is to use offset-course flight to the greatest degree possible, and to use orbiting only when the time to be expended is greater than the former technique can handle. The two methods must overlap so that no condition can exist when neither can be used. It is therefore necessary to set up certain criteria as follows:

(l) Maximum valueV of .R for which an indirect pat tern may be started=2- v (2) Minimum range for starting approach (radius ofl circle A in Fig. 2)=l2 miles.

(3) Minimum value of range for which will be determined=21/2 miles.

(4) Acceptable range of R when r=21/2 miles within which approach may be considered satisfactory=0.8. to 1.2.

For a 240 mile-per-hour aircraft at minimum startingy start its approach only when this condition holds, sitlnations where R 1.0 should be rare. L Iowever,` atl-lY ing td. Under such conditions @E R l v di T d where v is the actual speed and v' the value set in. It is necessary to set 1 equal Ato a function which will bring about the desired corrective action. Using the function there will result a desired air speed of and instructions to effect this can be transmitted to the aircraft. It will be noted that this operation requires use of radar determined speeds if rate data is to be transmitted. Previously these had not been used because of the uctuations likely to be present. However, when R l.0, planes will be travelling radially, the velocity variations will be at a minimum, and the data should be usable.

Throughout the procedures described above, continual altitude adjustments are also made. Although most aircraft can lose altitude at a rate greater than 500 feet per minute without difficulty, in general it is poor policy to require them to do so. Since collision avoidance may require level or climbing flight over some portion of the pattern, it is advisable to make the standard glide path more gentle, for example, 200 feet per minute. The following can therefore be set up as basic altitude rules:

(l) If the altitude (i about 200 ft.) is greater than 20015, the plane should descend at a rate of 500 feet per minute, and

(2) If the altitude (i about 200 ft.) equals 200ts, the plane should descend at 200 feet per minute.

(3) If the altitude is is less than 200ts, the plane should climb at 20() feet per minute.

(4) If the altitude is less than 100i', the plane should climb at a rate of 500 feet per minute.

(5) If the altitude is above 50015, an emergency signal may be transmitted in an effort to increase the rate of descent.

(6) If the altitude is at any time greater than lOOOtS, the run is a failure and must be restarted.

The aircraft has now been provided with instructions or data for suitable control of the basic flight parameters, course, air speed and altitude. The only remaining function to be performed within this sequence is to prepare the plane for its final approach. This involves decreasing air speed to the final approach value and lowering flaps and landing gear. These comprise a series of events so interrelated that a single instruction will be adequate to start all necessary action. If an instruction to Prepare for Final Approach is issued when an aircraft is 2%., to 3 miles from the turn-on point (r=21/z to 3), all types of planes should have completed the necessary action within a few seconds either before or after they pass that point. `The next and final instruction' to be transmitted during the Second Sequence can be given when planes are 1 to 2 miles from the turn-'on point; it will simply inform them that they are cleared for a final approach and that they should switch (or willv be switched) to the appropriate landing aid.

Since the decrease in air speed is not started until 3 miles before the turn-on point, while the transmission of ts/td information ceases when r=21/z miles, the former action will not have time to produce any appreciable effect on the latter data. There is still a question regarding the differences in aircraft characteristics having a sufiiciently large effect on the final approach air speed (and the decrease thereto) to promote danger of conflict. Unfortunately, aircraft will have varying approach speeds and the planes with the slower speeds will lose time during both the decrease and the approach with respect to faster planes. Furthermore, the fasterf aircraft cannot be slowed down earlier in the flight pattern, as flying any distance at final approach speed introduces danger of engine overheating. These factors may produce time variations as large as 1 to 11/2 minutes between planes. This will definitely limit either the types of planes which can use an air field or the landing rate which can be established without danger of conict at either the turn-on point or the airport. The best that can be done is to have slightly different scheduled turnon point arrival times for the fast and slow planes and thereby split the time variation equally between the turnon point and the air field. Thus, a slow plane might be scheduled to arrive at the turn-on point 15 seconds ahead of the normal arrival time, since during the final phase it will lose 30 seconds with respect to a faster aircraft.

Summarizing the actions of a DATAC unit during the Second Sequence:

(l) Three basic quantities are determined as a func tion of aircraft position and speed. These are the direct pattern heading (d), distance (d), and flight time (fd) (2) From these, the earliest unoccupied arrival time at the turn-on point for which the time-to-go exceeds the direct pattern flight time td is selected, and this initial time-to-go is diminished in step with the passage of time to continuously provide the remaining time-to-go (ts) until the selected arrival time. In the case `of emergency aircraft, the earliest arrival time, occupied or unoccupied, that meets the above condition is selected.

(3) Depending on the ratio R=t,/td, either an offset angle, or orbiting (to be followed eventually by an offset angle), is determined. The offset angle is either added to or subtracted from pd depending on aircraft position, and the resulting angle rpo is the course to be flown.

(4) When R 1.0 velocity instructions are transmittedY directly to the plane so that it will achieve a ground speed v0=v/R2.

(5) Throughout the operation, altitude is adjusted so that the plane will approach a ZOO-feet-per-minute glidepath.

(6) Failures, which will require restarting the operation, will occur whenever specific altitude or ts/td ratio limits are exceeded.

(7) Near the end of the Second Sequence, instructions are transmitted to prepare aircraft for the final approach and to transfer to the final landing aid.

T hrd Sequence As mentioned previously, interest in the Third Se quence is confined entirely to the problems which mayv arise when an aircraft misses an approach in some manner. start the whole operation with theFirst Sequence. After the Second Sequence therefore the First Sequence should be repeated; but this time the equipment should be kept inactivated unless a suitable signal from the final'approachsystem isi-received:

The simplest procedure in this situation is to re-l j, DATAC design The major components of a DATAC computer arez' (1) Master Sequencing Unit (2) First Sequence Unit (3) Second Sequence Unit consistingof:

(a) Position-Course, Distance and Time Computer y (b) Schedule Computer l y y y (c) Schedule Correction Computer l (d) Signal Selector Unit (4) Third Sequence Unit The Master Sequencing Unit Vis most simply described after considering the various other sections of the DATAC. For ease of understanding, however, it is desirableto present a brief account of its functions beforehand. These functions are: n

(1) Based on thersituation at a given time,'the unit eitherv remains set on a given Sequence orit will move to the next Sequence.

(2) When set on a given Sequence, the unit makes the necessary connections to permit the components'of the Sequence Unit assigned to that Sequence to function and theoutputs of that unit to be transmitted.

.= (3) When set on a given sequence, the unit preventsl the wcomponents of all other Sequence units from operatd ingyholds these components in a suitable Ready posit tion; and prevents false results from being transmitted.

F rst Sequence Unit The functions of the First Sequence Unit are: (1);To permit aircraft to move to the second sequence only when they are outside both Areas A and B and are within specified altitude limits.

(2) To give courses of 150:00 to aircraft in Area and pf-:270 to aircraft in Area B. p

(r3) To instruct aircraft with altitudes (feet) above 1200+200r (miles) to descend at 500 feet per minute while orbiting; to instruct those below lOOr to ascend at 500 feet per minute While orbiting.

The general principles used in the First Sequence Unit are:

(l) The presence of aircraft in Areas A and B are indicated by a short circuit established across suitably shaped, solid contact areas.

(2) The altitude limits are generated by two linear potentiometers mounted on the rotating range shaft, and the output of these is compared, in a simple electronic circuit, with the actual aircraft altitude.

.The details of the First Sequence Unit are shown in Fig. 6. Terminals 1 2 and 3 4 of the First Sequence Unit are connected to the Master Sequencing Unit. When thereis .a closed circuit between Lterminals 1 2 the .Mas ter Sequencing Unit holds the DATAC on the First Sequence. Whenever the `DATAC is on the First Sequence the Master Sequencing Unit applies a voltage to terminals 3 4 which energizes relay K3 land permits the outputs of the First Sequence Unitto behpassed to the signal selector unit.

The azimuth and range rof the aircraft, both measured from the turn-0n point, are derived from a tracking unit of the volumetric radar set (Fig. l) and applied as angles of rotation to shafts 25 and 26, respectively. If r is equal to..or less than theradius ofArea A (Fig. 2).-

"Ifthefaircraftris in Area B the-Values 0f-.0 and Ili'llz besuch. thatfth. Area., A www .27 Y are 012911: and 111i- A'IfeaB" contacts'` 28 are iclosed.r Thedesignsof f the Area B contacts are shown in Figs. 7a and 7b. Closureof contacts 28 actuatesyrelays Kza and Kb. Actuation of K2,l closes the circuit between terminals 1 2 and holds the DATAC in the First Sequence. Kzb connects the slider P1 through Km, to the SignalnSelector'Unit and applies thereto a direct voltage equal to the angle -9. As will be seen later, the Signal Selector Unit adds -l-0 to this angle to produce the required course 0=270.

Minimum andmaximum altitudes for any particular value of r are established by D.C. voltages supplied by P2 and P3 the moving contacts of which are actuated by the r-shaft 26. The output potentials of P2 and P3 are applied to the grids of Vlb and V28, respectively. A positive D.C.. voltage proportional to aircraft altitude is supplied by the volumetric radar set to terminal 29 and thence to the grids of Vla and Vgn. If the aircraft altitude is above the minimum altitude represented by the voltage on Vu, the current ow through i the common cathode resistor 30 due to Vn,l is suiiicient to maintain Vn, in cut-off. However, if the altitude is below the minimum established by P2 the current ow in resistor 30 due-t0A Vla is insufcient to bias Vlb below cut-off so that theconduction of this tube actuates relay K4. Closure of contacts K4., produces a connection across terminals 1 2, holding the DATAC in the First Sequence. Closure of contacts K4., closes the circuit between terminals 31 indicating that the altitude is to be increased at a predetermined rate. Closure of contacts K4b closes, through Kab, the circuit between Orbit terminals 32.

If the altitude of the aircraft is below the maximum established by P3 the voltage on the grid of Vzb will be insuiiicient to overcome the bias on this grid due to the Vga currentl in resistor 33 and V21, will be maintained in cut-olf. However, if the altitude exceeds this maximum the voltage on the grid of Vm, will rise above cut-off and relayK5 will be energized. Closure of contacts Km establishes a connection across terminals 1 2 to hold the DATAC in the First Sequence. Closure of contacts K5c establishes, through K3c, a connection across the terminals 34 indicating that the altitude is to be decreased at a predetermined rate. Closure of contacts K5b establishes, through Kab, a connection across Orbit terminals 32.

When the aircraft has satisfied the conditions of being outside Areas A and B and within the prescribed altitude limits for its range, the connection between terminals 1 2 is broken and the Master Sequencing Unit (after a brief delay to ensure there has been no temporary malfunction) moves automatically to the Second Sequence. During the Second vSequence relay K3 is deenergized by the Master Sequencing Unit.

Second Sequence Unit The Second Sequence Unit performs the seven functions outlined previously at the end of the description of the Second Sequence. `The Second Sequence Unit of an individual DATAC is shown in block form in Fig. .8.

' receives the aircraft azimuth 0 and range r from the pattern course'and the bearing of the turn-on pointfrom the aircraft is" determined. If vis addedl to! Actuation of or subtracted from (when 180 0+180, the result S d.

For a specific value of azimuth,

function of T Since both mx and rmm are functions of 0, this can be written Within the second and third quadrants, the physical interpretations of some of these functions are:

Quadrant II Quadrant III Function K cos (f1-90) 180-0 K (fr-0) The values of K and K are determined from the diameter of the final turn which in this case is 6 miles. In the rst and fourth quadrants the above interpretations do not apply and the functions in the computer are simply tted to empirical and calculated data.

The schematic diagram of the Position-Course, Distance and Time Computer is shown in Fig. 10. The computer receives 0 and r, in the form of angular displacements of shafts 25 and 26, from one of the tracking units of the volumetric radar set and the cruising speed v' is set in manually or may be obtained by radar also. In this figure unit voltages are used for the input voltages E4, E and E6 under which condition the proper scale factors for converting the nal voltages to degrees are 312.5 degrees and 21.1 miles per volt, respectively. A constant D. C. voltage E4 is applied across potentiometer P4 which is actuated by the shaft. The resistance characteristic of this potentiometer is shown in Fig. 11 and conforms to the function i109). The output of P4, which is proportional to 11(0), is applied across P5. P5 is actuated by the r shaft and has a response propor- -tional to l/r, its characteristic being shown in Fig. 12.

he output of this potentiometer, therefore, is a product equal to will have a wide range of output displacement.

maximum value which ca n attain beforey the Master Sequencing Unit switches to the next sequence is 3.0, but this is physically an almost impossible event. f

vPotentiometers P6, actuated by the Servo No.V 1 shaft, and B7, actuated by the 0 shaft, complete the calculation of The output of P6 is proportional-toV This Y The 12 and that of P7 is proportional to 13(0). The output of P7, therefore, is the product which equals The characteristics of P6 with respect to both the displacement of Servo No. 1 and its input voltage is shown in Fig. 14, and that of P7 in Fig. 15. The situation wherein an aircraft is within' the area described by the radius of the nal turn corresponds to the case where There is no single physically correct course for such a condition, so the curve of P6 has merely been extended in a manner to insure that planes will be directed beyond the limits of this area. Although travel inside the tum will probably occur frequently, the distance traversed should always be small; consequently, this procedure should be sutlciently accurate. Since must be either added to or subtracted from 0+180, both positive and negative values of the D. C. voltage E5 must be available. The proper one of these is selected by switch SW1 which is controlled by the position of the 0 shaft. In either case the voltage must equal 312.5 on whatever voltage-degree scale is used. Since, as already mentioned, (i4-180 will be added to the electrical course signal in the Signal Selector portion of the equipment, this action will not be necessary at the Position-Course Computer stage. Whenever relay K6 is closed by the Master Sequencing Unit, is transmitted to the Schedule Correction Computer where the next step in determining the correct course takes place.

Although the rst steps in computing td are similar to those for determining several more operations are required. These involve adding A, to r, and dividing the whole by the cruising velocity v. A. C. voltage E6 is fed to a Variac whose position is controlled by manually setting in v'. The output is fed to two transformers T1 and T2. T1 is a one-to-one transformer whose output, E7, is proportional to Maximum Range miles) w--v T3 has an output, E8 proportional to Maximum Ar (21.1 miles) whichiis applied to P8 actuated by the Servo No. l shaft. The output of this potentiometer is then applied to P9 actuated by the 0 shaft. The characteristics of P9 and P9 and the functions they represent are shown in Figs. 14 and 16, respectively. The output of P9 is the product of the two functions represented by the two potentiometers,

motlH-l] Y hv,

which equals Ar/ v'. Meanwhile El V7 is applied across linear potentiometer P10, actuated byv ther shaft, so that its output equals r/v. Since the transformer T1 is not grounded, the output of P10 can be added to Ar/v' and the sum will equal This result is then fed to the Main Schedule Computer. y

.. ansiosi;

f, 13 Y common area is necessary to ensure that no more than one aircraft will select a' given time of arrival at the turnon point. The second distinguishing characteristic is that the main action will take place only once during a normal operation, and this action `must start at a specific time and from a specific condition (in contrast to the other components which may run continuously, with the Master Sequencing Unit directing when to use their outputs). The special requirements of the Main Schedule Computer tend to make its operation, though not its equipment, somewhat more complicated than that of the other components ofthe system. Y

The operation of the Main Schedule Computer is primarily based on two types of equipment--a clock driven potentiometer anda group of continuously rotatable stepping switches. The potentiometer contains a large number of taps (20 or more). During normal operation, a voltage proportional to the time-to-go until one of the permissible times of arrivalv is available at each tap. The stepping switches, one of which is required for each DATAC unit in the system, must have at least four banks of steps, each bank containing onel step for each potentiometer tap. One ofthe banks is used for obtaining the ts voltages; one for the correct-altitude voltages; and two for the continuity current.

The general principlesl of operation are as follows:

(l) The clock-driven potentiometer delivers to the corresponding steps of each stepping switch voltage (ts) proportional to the scheduled time-to-go Values. These voltages increase in the direction in which the switch steps, the voltage diierence `between two adjacent steps being proportional to the established minimum separation time at the turn-on point. The ts voltage on any given step decreases with time as the clock mechanism operates.

(2) The stepping switches are arranged so that a short circuit is produced across each pair of continuity-current steps except the pair ofthe steps in which the ts wiper is resting. At the step, two continuitycurrent wipers permit the sampling and/ or breaking of the continuity-current by outside elements.

(3) The taps of the corresponding continuity-current steps of each stepping switch are connected in series. If a power supply is then connected across the outside continuity-current taps, a current will `only flow through those steps on which no ts wiper is resting.

(4) The restf condition of the stepping switch has the ts wiper on its lowest possible value. When ordered by the Master Sequencing Unit, the switch starts advancing to successively higher values -ofV ts and continues until the value of ts sampled is higher than that of td, the direct-pattern ighttime. If at this step the con tinuity current is absent (thereby indicating that another aircraft has received that ts), the switch advances to the next step. If, on the other hand, a continuity current is present, the wiper remains at that step, while external circuits break the continuity current to prevent another plane from selecting the same position at a later time.

(5) Emergency aircraft are provided with an artificial continuity current. rlhey will, therefore, stop at the rst step for which ts td. Conicts resulting from this action are resolved after selection of this earliest possible arrival time. f l

The design of the Main Schedule Computer is shown in Fig. 117. The clock-driven potentiometersPu and P12, the power` supplies E0 4and E10,and' the continuity current power supply Ee arecommon to the whole DATAC system. All the remaining elements, unless otherwise noted, are duplicated for each unit. Stepping switch K is continuously rotatable and has four banks of contacts, namely: the ts bank 35, the continuity current banks 36-37 andthe altitude bank 3S. Each ts contact is suppliedwith voltage that cyclically varies from a maximum value, representin'g'BO minutestthe maximum ts), to zero. The voltage between adjacent ts con- ,s 1.4 tacts at all times represe i tion timebetween,timesgof-arrival at thepturn-,o'n point; in this case 11/2 minutes. These voltages aresupplied from voltage source E0 by means of clock driven potentiometer P11 shown in Fig. 11711.A Similar voltages are applied to the altitude contacts38 of K10 by voltA age source E10 and clock driven potentiometer P12,0also shown in Fig. 17a. E10 is proportioned in this casette equal 1500is (max.) feet. Since, in this example, the maximum value of is is 30 minutes, the amplitude of E10 is made such as to equal l500 30 or 45,000 feet.'` The voltagev E10, appearing at the altitude Vwiper 39, therefore varies cyclically from a maximum value, rep-Y resenting 415,000 feetMto zperorandY at all times equals 1500ts. The voltage is suppliedto the Signal Selectorv Unit'v for use in a manner, to be described later, V 4

. The cdntinuitycurrent contacts. 35v-36 are bridges in all positions except that corresponding to the position of the ts wiper 40. At this position a continuity cur rent sampling circuit is introducedl by contacts 41.V For each value of ts the continuity contacts of all K13 switches. are connected in series across voltage E0. C

The continuity current for the step on which the ts wiper is resting must flow through relay K9 and the`b contacts of K11 before it can pass to the contacts of the next stepping switch.V K0 may therefore be used to test for the existence of this current, While operation of K11 maybe used to interrupt it.. Manual switch SW3' may be used to bypass the system of steppingswitches and thereby produce an artificial continuity current for emergency aircraft, while K14 is controlled by the Master Sequencing Unit to perform the same function during theV lst and 3rd Sequences. The latter action is necessary to insure that all switches rest on the same step, the lowest, when they are not in use. The process for accomplishing this will be described later.

During the Second Sequence K0 is held closed bythe Master Sequencing Unit, thus permittingrboth t0 from the Position-Time Computer and the sampled value of ts from contact 40 of K13 to be applied to dividingV` Servo No. 2. The output displacement of this servo is a function ofthe ratio of ts/t,1=R. 1 At the start of operation, which is initiated by appli` cation of a voltage to terminals 4-5 by the Master Se'- quencing Unit, the values of ts, and therefore ts/td, will be low. Under these conditions SW2, actuated by Servo No. 2, is in its lower position (R 0.l). K10 is now.. energized, by E0, and K0 and K11 are deenergized. The stepping solenoid of K13 therefore receives impulses from E0 through K10 and K10, and advances. This continues until .fs/td l.0, at which time SW2 moves to the upper position, deenergizing K10 and opening the K13 solenoid at the contacts of K10. The first condition of the Schedule Computer, that tS be greater than td, is now fulfilled and the stepping, solenoid receives no further pulse via the controls of K10. l 1

Although K10 is deenergized by the operation of SW2, K11 is not necessarily energized since Kga maybe open due to the absence of a continuity current. With both K11 and K0 deenergized, impulses from Ed reach K13 through Kgb and K11a and step this relay once for each pulse. When contacts 41 of K13 nd a closed ts circuit a continuity current flows through K0. With this relay energized current from E0 flows through KM', K11 and the upper contacts of SW2. When K11 is thus energized contacts K11c bypass contacts Kga, making the energiz'ation of K11 independent of the continuity current. The operation of K11 both prevents further impulses lfrom reaching K10 via K11,L and breaks the continuity cur rent at K110, thereby reserving the step on which'K13is resting. The second condition-that the selected ts be free from conflicts-is therefore met. Three problems still remain;

(l) Resolving any conflicts resulting from the sched-vv uling of an emergency aircraft,

(2) Ensuring that K13 starts advancing from the proper position, i. e., the lowest values of ts, and

(3) Ensuring that suitable action will be taken whenever a failure occurs (R or altitude limits exceeded).

The first of these is handled by SW.1 which is common to all units. When an emergency aircraft has been assigned a DATAC unit the switch SW3 for that unit is closed, which bypasses the various K13 switches and produces an artificial continuity current fory the assigned unit.V Under this condition the K13 switch for the assigned DATAC advances to the first value of ts that is greater than td and stops thereon due to the opening of SW3 and K10, SW4, which has contacts for each DATAC, is then opened for one impulse of V11. This can be-easily accomplished manually by observing light 32 which ashes in synchronism with the E11 impulses. The interval between these pulses is about live seconds in order to allow sufficient time for dividing Servo No. 2 to reach its correct position following each new position of the associated stepping switch K13. Opening of SW.1 deenergizes the various relays K11 and, in effect, requires a new sampling of the continuity currents by all units. However, except in the case of an aircraft havmg the same ts as the emergency plane, continuity currents will be present and deenergization of K11 will be accompanied by energization of K3 which will prevent -stepping impulses from reaching K13. With K3 energized a circuit is completed through K3a for the reenerglzation of K11 when SW1 is again closed. Recuergization of K11 breaks the continuity current at K11b, deenergizmg K3, and completes the K11 holding circuit at K11c. For the aircraft with the same ts as theemergency plane, however, the interruption of its continuity current, due to the closed SW3, will start a rescheduling process for this plane. This is brought about by the fact that, with regard to the relays associated with the @ATAC assigned to the plane, the absence of a conttnuity current due to closure of the SW3 switch assocrated with the DATAC of the emergency plane results in a'deenergized K9 which prevent K11, by the open circuit at Ksa, from being reenergized upon reclosure of S W.1. With K11 deenergized stepping impulses are applled from Ed through K3b and K11 or to K13 causing this relay to step until a continuity current is found, when stepping will cease due to the opening of Kgb provided SW2 1s in its upper position (R 1.0). Should this switch be in its lower position (R l.0), stepping will continue through K10 until a continuity current is found at a ts that 1s greater than the td for the particular plane.

With regard to the second of the above problems, when the operation reaches the end of the Second Sequence after a successful approach the value of R is close to 1.0 and the values of ts and td are small. At the end of the Second Sequence the Master Sequencing Unit simultaneously removes voltage from terminals 4 5 and applies voltage to terminals 3 4. Removal of voltage from terminals 4--5 deenergizes K3. The effect of this is to apply Eg and 2/3 Eg to dividing Servo No. 2 via Keds to remove the t3 voltage from Servo No. 2 at KS3, to remove the ts voltage from Servo No. 2 and to apply it to the grid of V3 at KSC, to break the K13 stepping circuit at K3, holding K13 in its last position, to close relay K3 after a slight time delay, and to close relay K14. The application of Eg and 2/3 Eg, which is equivalent to having R=0.66, causes SW2 to move to its lower contact closing relay K13. This relay bridges contacts Kgb, which are now open due to the energization of K3 by closure of K11, and establishes a stepping circuit for K13 which includes the contacts of K10, contact a of K11 which was deenergized by the action of SW2, and the contacts of K15. As stated above, ts at this point has a low value which is approaching zero. If is has any value above zero, however, K12 is energized thereby with the aid of the amplification of V3. Energization of K12 prevents the application of V1 to K13. This was previously prevented by K1, the slight delay of this relay being for the purpose of preventing the-application of E1 to K15 until K12 has had time to operate. When ts, which continues to decrease drops to zero, K12 is deenergized and E1 is applied to K15. Closure of the contacts of this relay applies a stepping pulse from Ed to the K13 advancing this switch one step. Since the next higher value of 1s will have not yet reached zero, being separated from the preceding value by the interval of 11/2 minutes, K12 and consequently K15 will again be energized preventing further stepping of K13 until the new value of ts has decreased to zero at which point K13 advances to the next higher step, and so on. This process ensures that whenever the Schedule Computer is called upon to function switch K13 starts searching from the lowest value of ts.

Regarding the third of the above problem, since it is desirable to give aircraft which fall behind schedule (R l.0) a chance to catch up, SW2 is constructed to permit this. If it has once moved to the upper position (R l.0), it remains there until R drops below 0.7. Before this happens, the aircraft under control will have been deemed a failure in the Schedule Correction Computer, subsequently described, and the Master Sequencing Unit will be moved to the First Sequence. It is quite possible that the operation will return to the Second Sequence before the ts at which K13 is resting will have decreased very much. This will cause no difficulty, as the new ts to be selected will have to be at least as great as the old one was. No special action for such failure is therefore required of the Schedule Computer.

The Schedule Correction Computer is shown schematically in Fig. 18. The major functions of this computer are the final determination of the correct course (cpo) and ground speed (V3) to be own. In addition, however, it also establishes the existence of failures, and provides data to the Master Sequencing Unit for sequence control. More specifically these functions are:

(l) Whenever R 2.0, orbit instructions are sent to the aircraft under control. l

(2) When R 2.0, a suitable offset or schedule correction angle ,Bis added to or subtracted from :L-, defined in Fig. 9.

(3) When R 0.98, velocity instructions to establish a ground speed v3=v'/R2 are transmitted.

(4) When r 2 miles, the operation is moved to the Third Sequence.

(5) Failures are indicated when R 0.7. Failures are also indicated if l.2 R 0.8 when r is less than slightly over 2 miles.

The computer receives the following data: 0, as a rotation of shaft 25; r, as a rotation of shaft 26; cruising speed v', as a rotation of shaft 42; and voltages representing tf1, ts and The offset angle ,8 is produced by P13, which is actuated by the R shaft 43. The characteristic of this potentiometer is such as to provide a desired relationship between R and such as shown, for example, by pattern 1 in Fig. 4a. To permit addition to i5, this potentiometer is supplied with a oating voltage E11 through SW5. Switch SW3, controlled by the 9 shaft, determines whether a positive or negative E11 will be used. Whenever 9 240, it provides a positive voltage and continues to dol so until 0 decreases through 120. Negative voltage is supplied whenever 0 120 degrees and remains until 0 increases through 240. This change of the sign of switches the general direction of travel of the control led aircraft. When ii has been produced, several other conditions must be met before it can be transmitted to the Signal Selector:

1) R must be less than 2.0 (SW3 and SW10 in righthand position).

(2) Range must be greater than 2+ miles (switch SW1 in left-hand position, K13 not energized).

(3) Master Sequence Unit must be in Second Sequence (K13l1 closed).

Whenever (l) above is `not met, SW1@ will be in the left position and the Orbit circuitV will be closed through Km. 1f condition (3) is not met SW6 closes causing the Master Sequencing Unit to shift control Vto the Third Sequence.

Velocity instructions are obtained from P1.; and P15. The former, which is actuated bythe v' shaft L52, produces a voltage proportional to v', while the latter, which is actuated by the R shaft, produces the function l/ 18 this time. The schematic diagram of this unit is shown Fig. i9 and its functions are as follows:

(l) During the First Sequence only, an open circuit between terminals 1 2 (see Fig. 6) requires the Master Sequencing Unit to move to the Second Sequence.

(2) During the Second Sequence only, a closed circuit between terminals 6 7 (see Fig. 18) requires the Master Sequencing Unit to move to the First Sequence.

(3) When on the First Sequence the Master Sequenc Their product, V0, is sent to the Signal Selector whenever it) ing Unit can not switch to the Second Sequence unless VR 0.98 (SWB closed), KM; deenergized (R 2|-miles) manual Start Switch SWUL has previously been closed or and Kw is energized. unless contact has been made across terminals 8 9 either Sequence control is provided by SW6 and by the failure by the Schedule Correction Computer (Fig. 18) as the system. When r decreases below 2 miles SW6 is closed result of a failure during the Second Sequence or bythe thus presenting a short circuit to the Master Sequencing final landing aid as a resuit of failure during the final Unit through terminals 6 7, causing transfer to the landing operation. Third Sequence. The failuredata is provided by two (4) When on the First Sequence, power is supplied sets of contacts 44 and 4S on the R shaft. Contacts 45 through terminals 4 5 to Operate relays K3 in the First close when R 0.7 while contacts 44 operate whenever and Second Sequence Units (Figs. l5, 17 and 18). 1.2 R 0.8. Since current through the latter must also (5) When on the Second Sequence, power is delivered pass through the contacts of Kw, its data will be effective through Vterminals 4 5 to operate relays in the Second only when R 2+ miles (Km energized). Subject to Sequence Unit (Figs. l0, 17 and 18). this condition closure of either set of failure contacts The Master Sequencing Unit comprises a rotatable step 44 and 45 causes Km to be operated by Ei. Km has three s switch K2@ having twoV positions marked Sequence l and contacts: one (a) to transmit a failure signal to the air- Sequence 2. The voltage Ej, when applied to K20, causes craft, one (b) to present a short circuit to the Master the switch to move to the other position. Assume that Sequencing Unit through terminals 6 7 and aA third (c) the computer is in operation on the Second Sequence. to operate a Start circuit through terminals 8 9. The If this Sequence is completed successfully SW6 (Fig. 18) function of the latter will be further explained in concloses when r decreases below 2 miles. The resulting nection with the Third Sequence Unit. To prevent any connection across 6 7 allows Em to operate K23Vthrough failure actions during the First or the Third Sequences, contacts 2b of K22 which steps K20 to the Sequence l Kn is energized by the Master Sequencing Unit during position and the DATAC is finished with that particular these periods of operation. It is provided with a 30 aircraft. When the DATAC has been assigned to ansecond delay, however, to permit the failure signal to` the other aircraft start switch SWH is manually operated.A aircraft to be sent for that length of time even though This actuates K21 which is kept in an energized condition the operation has switched to the Third Sequence. by the holding circuit established through K21a and the The action of the Second Sequence Subcomputers may la contacts of K20. When the aircraft is in position to be summarized as follows: proceed to the Second Sequence the connection across Inputs Outputs Computer Item Source Form Item Form Destination T, 6 Tracking Unit Shaft displ. i6 D. C. voltage Sched. Correction Position-Course, Dls- Computer. f tance and Time. v Manual Setting Shaft displ td A.C.vo1tage Main Schedule td Pos-Time Comp. A. C. voltage t A. C. vo1tage .tSeivd Allowable values Clock'driven po- A. C. voltage Shaft displ. Sched. Correction Main Schedule.; s. tcntiomcter. Computer.

Y Lothar aircratt OtherVDATACS Breakincontinuty- 1500 t, D. C. voltage-.. SigilltSileptor Pos.tCourse Com- D. C. voltage ii D. C. voltage.-- Signal Slelgctor. Trpallilr'ig Unit Shaft displ Orbit Sgnal Closed circuit-.. Signal Selector. Schedule Correction Manual Setting Shaft dispL Failure Signal Closed Circuit Signal Selector `and.

. Master Seq. Unit. Dividing Servo Shaft dispL V0, Final In- D. C. voltage-.- Signal Selector struetions. (velocity).

Third Sequence Unit As already stated the Third Sequence is identical to the First Sequence and therefore the First Sequence Unit also performs as the Third Sequence Unit Whenfcalled upon to do so. Therefore, after completion of the Second Sequence, the Master Sequencing Unit returns tothe First Sequence, however, operation cannot proceed again to the Second Sequence unless a Start signal is received by the Master Sequencing Unit indicating a failure either during the Second Sequence or during the final landing operation. The Start signal takes the forrn of a short circuit across terminals 8 9 of the Master Sequencing Unit. This short circuit can be effected by the Second .Sequence Unit or the nal landing aid.

Mster Sequencing Unit terminals 1 2 is broken by the First Sequence Unit (Fig. 6) andafter a delay K22 releases. Stepping voltage is then applied to K2@ through K21b and K22, which moves the switch to the Sequence 2 position and places the Second Sequence Unit in operation. t

If a failure occurs during the Second Sequencerthe operation, in effect, is to automatically close SWU so that the aircraft can restart with the First Sequence and, when completed, proceed normally to Athe Second Sequence again. Failures occur when l.2 R 0.8, if r 2|miles, or whenever R 0.7. Either situation results inenergization of K12 (Fig. 18). Actuation of this relaybridges terminals 6 7, causing switch K20 of the Master Sequencing Unit to move to the Sequence 1 position, Vand also bridges terminals 8 9 which actuates Km thus placing the Master Sequencing Unit in condition to move to Sequence 2 when K22 is deenergized and its contacts close at the completion of the First Sequence. 

